This invention relates to catheter introducers, sometimes termed cannulas, and particularly introducers used for the positioning and manipulating of intra-vascular catheters known as angiographic catheters.
Angiography is a well known and valuable procedure employed to diagnose vascular and organ disease. It involves the introduction of a hollow tubular catheter into one of the major arteries or veins, such as the femora or brachial artery, and advancing and maneuvering the catheter into smaller or branching vessels which are to be studied. After the catheter is in position, a radio-opaque fluid is injected through the catheter into the vascular system to be studied, and an x-ray picture is taken of the thereby x-ray opaque vascular structure.
There are such techniques for introducing such catheters which include the so-called "cut down" method and various modifications of the so called Seldinger technique. The "cut down" technique involves surgically opening a vein or artery and introducing the angiographic catheter directly through the incision. This method inevitably involves the loss of blood through the incision and may also involve venous ligation and arterial repair. The use of this method renders it particularly difficult to employ the same blood vessel when multiple studies are indicated.
An alternative method of cardiac catheterization comprises a modification of the Seldinger technique in which a subcutaneous sheath is introduced into the lumen of a blood vessel: a hollow needle is inserted through the skin and into the lumen. Thereafter, a guide wire is passed through the needle and advanced up the artery. The needle is then removed, leaving the guide wire in the vessel; a sheath and dilator unit are then advanced over the wire and into the vessel and the dilator is removed along the guide wire. In this technique, any type of catheter can be inserted through the sheath into the vessel. To avoid excessive bleeding, and to insure against the possibility of an air embolism, this technique requires that the physician occlude the orifice of the sheath during catheter changes. Therefore, this procedure suffers from the risk of a blood clot migrating to the heart, lungs or extremities. It has been found that blood loss through the annular space between the sheath and the catheter is difficult to avoid. Both of the above methods have been characterized, especially if multiple studies are indicated, by venous thrombosis, subcutaneous hematomas and considerable discomfort to the patient.
One response to the above problems appears in the U.S. Patent No. 4,000,739 to Stevens, entitled Hemostatis Cannula. This invention involves the use of a certain arrangement of intermeshing disc gaskets in order to hold and/or manipulate the catheter within the sheath during angiographic or other catheterization procedures. The device of Stevens, while representing an improvement over prior art therebefore, is still awkward to use in certain situations and, as well, contains the risk of air embolisms, as was the case in the prior art before Stevens. Other pertinent prior art known to the inventor includes U.S. Pat. No. 2,844,351 to Smith, entitled Fluid Flow Control. This device does not solve the above problems in the prior art.
The present invention is believed to be properly classified in U.S. Class 128, Subclass 214.4; and Class 251, Sub-.
In the known prior art, there has not existed a catheter introducer that can accomodate any sized catheter. Also, those catheter sheaths known in the prior art have not had a good capability of sealing in both longitudinal directions of the cannula. In the prior art, such as Stevens, the atmospheric pressure seal of the sheath introducer against below atmosperic pressures has often not been favorable; therefore, leakage (air asperation) has, on occasion, been a problem.
Finally, during the withdrawal of the catheter, prior art devices have had a tendency to leak. That is, during withdrawal (and, on occasion, during advancement), the cannula often would not totally seal the catheter, i.e., a complete sealing in the prior art could occur only when the catheter was not moving relative to the cannula.
Further, in prior art catheters, the advancement of the catheter could not occur if the valve of the introducer was in a closed position.
It is to all of the above shortcomings in the prior art that the present invention is addressed.